The present invention relates to a corona discharger incorporated in electrophotographic image forming equipment and, more particularly, to a method and apparatus for positioning the corona discharger relative to a photoconductive element also incorporated in the equipment easily and rapidly.
A laser printer, facsimile transceiver or similar electrophotographic image forming equipment has a photoconductive element in the form of a drum or a belt, and several corona dischargers such as a main charger, transfer charger and separation charger arranged around the photoconductive element. The dischargers each effects a corona discharge between it and the photoconductive element to cause a discharge current to flow through the element for the purpose of depositing or dissipating a charge on the element. Generally, the amount of charge, for example, deposited on the photoconductive element has critical influence on the quality of an image to be formed on the element. Hence, the amount of charge, among others, has to be controlled with accuracy in order to form desirable images. The problem with a corona charger for the above application is that the particles of toner, paper dust and dust existing in air sequentially collect on and thereby contaminate the discharger, particularly a discharge electrode or wire thereof. Since this kind of contamination adversely affects the discharge, it is necessary to remove the corona discharger for cleaning or replacement periodically. However, when the cleaned or a new corona discharger is so set as to face the photoconductive element, it is likely that the positional relation between the discharger to the photoconductive element, i.e., the distance between the discharge electrode or wire and the surface of the photoconductive element changes. It follows that the distance between the wire of the corona discharger and the surface of the photoconductive element has to be adjusted accurately to insure an image having uniform density. For this kind of adjustment, it is a common practice to remove the photoconductive drum, for example, from the equipment and the set a false photoconductive drum, or jig drum, in place of the removed photoconductive drum. In this condition, while a charge current which flows through the surface of the jig drum is measured at axially opposite ends of the drum alternately, an adjusting screw provided on the front of the corona discharger is turned until the currents flowing through the opposite ends of the jig drum become equal to each other. After such adjustment, the cleaned or a new photoconductive drum is substituted for the jig drum.
The above-stated conventional procedure for adjusting the positional relation between the photoconductive drum and the corona discharger, i.e., the distance between the surface of the photoconductive element and the discharge electrode or wire of the discharger is extremely time- and labor-consuming and, moreover, inhibits the equipment from being operated until the adjustment completes.